Power converters are widely used in electrical and electronic devices. Certain devices, such as notebook computer, personal digital assistants (PDAs), cellular telephones, and other portable consumer products, require power converters that provide low standby power consumption in light or no load conditions. To achieve this, the power converters must have some intelligence for monitoring and reacting to various conditions during the power conversion, such as, for example, output voltage, over-voltage and under-voltage, standby or normal mode, power ON and OFF, etc. Furthermore, in some applications, it is desirable to have a very fast calculation time for an internal current controller loop in order to provide good dynamic performance.
Various systems have previously been developed and considered for providing control of power conversion in these kinds of applications. However, all of the various systems have been inadequate or problematic. For example, a purely analog control system, while fast, lacks the necessary intelligence; this results in significant power dissipation under certain conditions (e.g., light or no load). In contrast, a digital control system implemented with a simple microcontroller may have sufficient intelligence, but is too slow. A digital control system implemented with a more complex microprocessor (such as a digital signal processor or DSP) provides sufficient intelligence and very fast calculation speed (e.g., 10–100 μsec) but is not commercially viable for a real market product because it would be too expensive. Furthermore, the hardware in such a control system with complex microprocessor is too complex—i.e., a typical DSP has an 8-bit or 16-bit bus with external read-only memory (ROM), random access memory (RAM), analog-to-digital (A/D) converters, and digital input and output ports.
What is needed is a power converter with a low-cost, intelligent, and fast controller.